The present invention relates generally to a non-aqueous electrolyte secondary battery making use of lithium ions, and more specifically to a battery improved in terms of charge-and-discharge performance by the addition of a specific material to a non-aqueous electrolyte.
With the recent increasing prevalence of portable electronic equipment such as portable phones, camcorders and notebook PCs, there are increased demands for batteries having high energy densities, especially non-aqueous electrolyte batteries. In particular, rechargeable lithium ion batteries of great safety are now widely used as batteries of small size yet high energy densities.
To allow non-aqueous electrolyte batteries such as lithium batteries, lithium secondary batteries and lithium ion secondary batteries to have high battery performance, it is of vital importance to inhibit reactions of electrodes with electrolytes. It is particularly important to inhibit the reaction of an anode with an electrolyte because the anode going down to very base potentials is likely to react with the electrolyte. This has some considerable influences on battery performance, especially battery capacity, battery storability, and secondary battery's cycling characteristics.
Thus, many solvents less susceptible to battery degradation due to reactions with anodes or their combinations are now investigated for non-aqueous solvents for non-aqueous electrolyte batteries while reactivities with anodes in particular are taken into account. Other considerations required for what solvent is selected are solubilities of electrolyte carrying salts, reactivities of electrolytes with cathodes, ion conductivity, and costs.
For non-aqueous solvents for lithium ion secondary batteries, organic solvents such as ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate, .gamma.-butyrolactone, methyl propionate, butyl propionate and ethyl propionate are used singly or in combination of two or more.
There are also many attempts to incorporate specific compound additives to an electrolyte and thereby improve battery performance.
Although depending on the type of the electrolyte used, however, it is often impossible for an anode material to make full use of its own performance due to the reaction of the anode with the electrolyte. A problem with this case is that battery performance, especially battery capacity, battery storability and secondary battery's cycling performance remain low.
It has also been proposed to add additives to electrolytes so as to inhibit the reactions of anodes with the electrolytes. However, a problem with these additives is that some additives thereof have adverse influences on not only the reactions of the anodes with the electrolytes but also battery reactions, failing to obtain voltages or currents that batteries have to provide.
JP-A 8-96852 discloses a battery using an anode comprising a material capable of doping or dedoping metal lithium or lithium, with vinylene carbonate incorporated in a non-aqueous solvent. When the vinylene carbonate is applied to a battery comprising a carbonaceous material anode, however, no sufficient battery performance improvement is achievable due to insufficient film formation capabilities.
An object of the present invention is to provide a battery making use of lithium ions, in which the reaction of an anode with an electrolyte can be substantially inhibited with no degradation of battery performance.